There exists an image forming apparatus which can change, when switching the conveyance speed of a sheet, the speed ratio of the conveyance speed of a sheet by a conveyance device conveying the sheet towards a fixing device to the conveyance speed of a sheet by the fixing device. On the other hand, in order to reuse a sheet, there exists an apparatus which heats and presses a sheet at a color erasing temperature higher than a fixing temperature using a fixing device to erase an image formed on the sheet. If the sheet is heated and pressed at a high color erasing temperature to erase an image, paper wrinkles occur easily on the sheet. Therefore, it is necessary to prevent the paper wrinkles occurring on the sheet when the sheet is heated and pressed at a high color erasing temperature.